This invention relates generally to implantable medical devices and more particularly, it relates to an implantable cardiac defibrillator employing an improved waveform digitization network for converting analog ECG heart signals from the atrium and/or ventricle into a sign/magnitude digitized signal plus a channel identifier bit, which is achieved with very low power consumption and without crosstalk between the channels.
In recent years, there has been substantial progress made in the research and development of defibrillating devices for providing an effective medical response to various disorders, such as ventricular fibrillation. Research effort has also been made toward developing improved sensing techniques for reliably monitoring heart activities so as to determine when a defibrillating high energy shock is required.
One of the techniques of the prior art for determining when ventricular fibrillation is present employs a probability density function, which is implemented with an analog approach. Such a technique, utilizing the probability density function, is disclosed in U.S. Pat. No. 4,202,340 to Langer et al. However, it has been experienced that the prior art probability density function detector can be "triggered" indicating a fibrillation of the heart even when there is a nonlife threatening condition. It has therefore been determined that there is a need for an implantable cardiac defibrillator employing an improved waveform digitization network for distinguishing between malignant tachyarrhythmias, such as ventricular defibrillation, and sinus rhythm.